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AB528 Microphone preamplifier / Re: 300 vs 1200 ohms?

« on: October 23, 2024, 06:30:55 PM »

What is considered “high impedance”.  Any specific mics you would use 300 on?

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AB528 Microphone preamplifier / 300 vs 1200 ohms?

« on: September 28, 2024, 07:20:05 AM »

I know, “use your ears”, but Im curious some specific mics you would use 300 with or 1200 with.  What is the general usage rule of thumb for choosing these?  I have all manner of mics, and 1200 just seems to be more open sounding in my limited testing.  

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AB528 Microphone preamplifier / Re: First power on burned resistors

« on: September 22, 2024, 11:50:39 PM »

Final update:  fixed
The di board diodes got me.  Oh well.  Works now and sounds pretty darn good. Di on bass sounds fantastic.  Mic pre is nice.  Saturation on line level signal is not as good as i had hoped for processing tracks, but mic level and di is the main intended use. 🍻

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AB528 Microphone preamplifier / Re: First power on burned resistors

« on: September 22, 2024, 10:16:49 PM »

Oh. Found something wrong.  Diodes on di board are not correct 🙄

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AB528 Microphone preamplifier / Re: First power on burned resistors

« on: September 22, 2024, 09:43:35 PM »

Ive replaced r33 and r34. What should I check before trying to power up again? 
I used my cranborne 500r8 before but think i will try my Lindell 510 500 rack this time as as the 500r8 is much more valuable.  
Could I rig up a 9 or 12v underpowered power supply from a wall wart just for testing point purposes before inserting into 500 rack?

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AB528 Microphone preamplifier / Re: First power on burned resistors

« on: September 22, 2024, 08:14:29 PM »

I checked and -91 is in q5, where it should be. Next?

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AB528 Microphone preamplifier / First power on burned resistors

« on: September 21, 2024, 05:09:16 AM »

Hello.  I was saddened to smell burning on first firing up my ab528.  I’ve built many 500 series and felt confident I understood and completed every step correctly.  The power was only on about 10 seconds and I see that r33 and r34 surely burned with possible discoloration on d7.  There is also a little melting on j2b.  The power Led never lit up. 
Every capacitor has correct polarity and magnifying glass couldn’t find any bridged solder spots or issues.  Please help!